1. Field of the Invention
This invention generally relates to switching devices for directive communications systems, and more particularly to a device for switching an antenna between a transmitter and receiver of a high-power, monostatic impulse radar system.
2. Description of Related Art
Radar systems may be classified into two general categories according to their geometrical configurations: monostatic and bistatic. Very simply, monostatic radar uses a single antenna to receive and transmit radar signals, while bistatic radar uses separate antennas, usually separated by distance comparable to a predetermined target distance, to accomplish the same.
Monostatic radar is the preferred configuration for target detection purposes for a number of reasons:
1) Monostatic radar, with its ability to scan in a hemispherical volume, is more versatile than bistatic radar, which is, more or less, confined to planar scanning. PA1 2) Monostatic radar, with its single antenna design, is likely to be less expensive to construct and maintain than a bistatic radar system with comparable detection ability. PA1 3) Monostatic radar achieves a dynamic range which is considerably more pronounced than bistatic radar.
One type of radar known as impulse, or ultra-wide band, radar transmits a very high peak pulse a few nanoseconds in duration. For years, radar designers have been trying to construct an operational, high-power, monostatic impulse radar, but have had limited success. At present, except for a few low-powered units operating in the UHF frequency range, impulse radar is confined to a bistatic configuration.
The primary stumbling block to the construction of a high-power, monostatic impulse radar has been the inability of radar designers to develop a switch which can operate at speeds rapid enough to provide adequate isolation between the transmitter and receiver. Without adequate isolation, the transmit pulse of the radar will leak into the receiver and render the system inoperable for target detection purposes.
In recent years, a few attempts have been made to construct a high-speed switch for an impulse radar system. U.S. Pat. Nos. 5,028,971, 5,155,352, and 5,177,486, for example, disclose the use of a photoconductive semiconductor switch (PCSS) to transmit sub-nanosecond pulses for impulse radar. A closer reading of these patents, however, reveals that the PCSS is used to generate sub-nanosecond pulses, not to provide switching between a radar transmitter and receiver.
Thus, a need still exists for a switch, or switching mechanism, which can operate at a speed fast enough to achieve a transmitter-to-receiver isolation sufficient to support a monostatic configuration for a high-power impulse radar.